Magnetic escapements have been known since the 1960s and 1970s and were the subject of the following patent applications: U.S. Pat. No. 2,946,183 in the name of Clifford, JPS 5240366, JPS 5245468U, JPS 5263453U. These devices are often difficult to incorporate in a watch, because of their bulk. Above all, they have the drawback of anisochronism, i.e. the maintenance of oscillations perturb the operation of the resonator, and the value of this perturbation varies with the amplitude of oscillation.
Patent applications EP 2891930 and WO2015 097172 in the name of THE SWATCH GROUP RESEARCH & DEVELOPMENT Ltd propose arrangements which can considerably reduce the perturbation caused by the maintenance of oscillations, so that its variation with amplitude becomes negligible. However, in practice it is difficult to design an ideally isochronous system, since an air gap of very small dimensions must be used, i.e. of negligible dimensions compared to the amplitude of oscillation of the resonator coupling element. In such situations, it would be useful to have a mechanism that makes it possible to offset the residual anisochronism produced by a non-ideal escapement.
There is another situation where such an isochronism correction mechanism would be useful. Indeed, it should be kept in mind that it is the whole oscillator, composed of the resonator maintained by the escapement, which must be isochronous. It may happen that the operation of the free resonator varies with amplitude, in other words by itself, i.e. without maintenance of oscillations, the resonator is not isochronous. In such a situation, it would be useful to be able to offset the anisochronism of the resonator by the anisochronism of the maintenance of oscillations.